The goal of this project is to elucidate individual muscle function during human walking. Walking requires precise coordination of the neuromuscular and musculoskeletal systems. The complexity of these has made it difficult to determine the functional role of individual muscles. Understanding how individual muscles operate during normal healthy walking has important implications for understanding neuromuscular impairments and designing effective rehabilitation strategies. Specifically, this project seeks to achieve two aims; to determine the relative contribution of individual leg muscles to 1) body weight support and 2) forward propulsion during walking. To achieve these aims, a novel combination of experimental perturbation and detailed musculoskeletal modeling and computer simulation will be employed. Experimental designs will involve combinations of load carrying and applied forces to alter the external demand musculoskeletal system in a known way. Experimental data will incorporated in to the development of dynamic models and computer simulations matching the experimental conditions. Individual muscle function will be determined through electromyographic (EMG) analysis of experimental data and predictions from the simulations. [unreadable] [unreadable] [unreadable]